The Nimrod R doesn't NEED replacing. Before XV230, the plan was an OSD of 2025, and the IPT were sanguine that the R1s, at least, could make that.
There are all sorts of compelling reasons why you might want to put the new Helix kit on a new airframe - not least because the R1s are, at best, 'cosy'. But while hosting the kit on an A300/310 (preferably with cargo door to ease conversion/installation) would mark an obvious step forward, a development MRA4 is still a Nimrod, with a Nimrod fuselage cross section, and the same cabin length. It therefore doesn't offer the one thing you'd really want in an R1 replacement, which is a bit more space - crew rest areas, a proper galley and toilet, etc.
The RC-135Vs that are supposedly to be procured are to be new conversions of KC-135Rs delivered to Block 10 standard. They will not be equipped with the existing Nimrod Sigint suite (Star Window) nor with the planned Helix. They will be USAF standard aircraft.
I know 'nothing', so all of this is open source, and much of it may be wrong, but I'm told that the RC-135V is more biased towards Comint than the Nimrod, with a little tactical Elint (the latter using the largely automated AEELS) and as such is better suited to the kind of ops we're seeing 'right now', but that the R1 is significantly better for the more traditional Sigint role (what the Yanks called PARPRO) against a 'formed state' enemy with formed forces and a structured air defence system, for example - as was required in the run up to Granby and Op Iraqi Freedom.
There are some concerns that replacement of R1 by RC-135 would necessarily result in some loss of capability (albeit with relevant gains in other areas) and especially a loss of the particular type of Elint expertise that 51 has built up over the past few decades - which emphasises highly experienced operators using their experience and manual tuning, etc.
There are a couple of niggling worries in my mind, apart from the possibility of a loss of national expertise and capability in this key area.
When we all thought that the Yanks were going to simply give us three -135s (they have a job crewing all theirs), it was hard to look a gift horse in the mouth. It now looks as though the RC-135V procurement will actually cost more than pressing ahead with R1/Helix would have done. Are we getting rid of the R1 for the right reasons, or because retaining a gen 1 Nimrod is politically untenable, or because after XV230, airworthiness is hanging by a thread.
The USAF is really hurting for tankers - and especially KC-135Rs. If there are three spare R models, sitting in the desert, god alone knows what sort of state they might be in.
The previous threads on this were at:
http://www.pprune.org/military-aircr...-aircraft.html
http://www.pprune.org/military-aircr...-aircraft.html
http://www.pprune.org/military-aircr...1-upgrade.html